1. Field of the Invention
The invention relates generally to the production of basic sodium and/or potassium aluminum sulphate from leach liquors of aluminum and sodium/potassium sulphates and to methods for producing newsprint with fillers and coatings of such aluminum and sodium/potassium sulphates.
2. Description of the Prior Art
Those who have handled, while reading, a magazine are likely aware of the amount of clay fillers and coating as well as the variation in the type and amount of such clay that was used in producing the magazine. Ash content can vary significantly from lightly coated (eight to twelve percent) publications to high quality, heavily coated (twenty-five to thirty percent) publications. The type and quality of coatings can also vary between cheaper magazines and high quality magazines such as The National Review, Scientific American, Playboy and the Smithsonian. Colored financial grades, such as typical checks and business forms, and the many different types of stationery and writing papers in use, generally contain around ten percent ash. This includes filler clay added to produce a smoother, higher opacity sheet, and such ash particles included are usually fairly small. Another waste grade is coated art books displayed often on coffee tables, which can easily contain twenty to thirty percent ash, mostly in the form of clay for coatings as well as pigments such as titanium dioxide.
Paper can be made with bleached or unbleached chemical pulps, mechanical pulps, chemi-mechanical pulps, or recycled pulps. It can include conventional additives such as sizing agents, fillers such as titanium dioxide, calcium carbonate, kaolin clay, or talc, and polymeric additives such as wet strength resins, polyamines or polyamide-amines, or polyacrylamide polymers or copolymers of acrylamide.
Non-cellulose coatings, filler clay and other products are added during paper manufacture or deposited on paper surfaces during processing or applied to paper in converting or printing operations to enhance a number of different characteristics, e.g., smoothness, printability, gloss, durability and paper protection. The range of formulation of the various materials varies greatly depending on the intended function of the paper. These can range from simple filler clay particles to tenacious chemicals and pigments. The amount of this material can vary from one percent to as high as fifty percent of the overall dry weight.
Basic paper pulp includes ground wood pulp, thermo-mechanical pulp, semi-chemical pulp, recycled mechanical pulps produced by de-inking of newspaper or magazines containing these pulps, etc. Such pulps are used singly or are mixed into a variety of well-known combinations. Within certain limits, a small amount of chemical pulp can be added to adjust the optical properties without adversely affecting the physical properties of the mechanical pulps.
Various pigments are commonly used for a filler, e.g., clay, talc, titanium dioxide, white carbon, calcium carbonates and urea resin fine particles, e.g., one-half to ten percent, by weight, that are added to the whole. Less than one-half percent usually causes poor opacity or oil absorption problems, and more than ten percent reduces the tensile strength or tear strength of the final paper product. Titanium dioxide is a relatively expensive material, and so is used sparingly.
Needle-shaped pigments are often used in coating layer pigments and include satin white, needle-form precipitated calcium carbonate, and Hong Kong kaolin. These pigments are mixed with binders and applied on the base paper as the coating color. Binders, for example, styrene butadiene latex, starch and starch derivatives, polyvinyl alcohol and cellulose derivatives are commonly used. However, the invention is not so, and several binders which are used as binders for paper making can be used, alone or in mixed form. The kinds and formulation ratios of binders affect the surface strength and absorptiveness of the pigments.
Conventional pigments include various kinds of silicon dioxide, activated clay, calcined clay, fine magnesium carbonate, various kinds of silicate, diatomaceous earth, urea resin powder, kaolin, talc, various kinds of calcium carbonate, titanium dioxide, and zinc white. Pigments with low oil absorption properties are used in mixtures with other pigments that have high oil absorption characteristics. Low oil absorptiveness pigments allow the coating color to be controlled better.
Kaolin clay, the crystal form of which is rhombohexagonal (hexagonal plate), is usually used as a major pigment for the coating layer of common coated paper. Because of the crystal form of kaolin clay, kaolin particles have a tendency to be in the parallel orientation under the smoothing treatment, and to give a highly glossy surface.
Paper and paper board are typically made from "thin stock", a dilute aqueous suspension of cellulose fibers. Alternatively, the thin stock is passed through one or more shear stages, such as cleaning, mixing and pumping stages, and the resultant suspension is drained through a wire to form a sheet, which is then dried. The thin stock is generally made by dilution of a thick stock that is formed earlier in the process. The drainage to form the sheet may be downwards under gravity or may be upwards, and the screen through which drainage occurs may be flat or curved, e.g., cylindrical.
It is common to include various inorganic materials, such as bentonite and alum, and/or organic materials, such as various natural or modified natural or synthetic polymers, in the thin stock for the purpose of improving the process. Such materials can be added for diverse purposes such as pitch control, de-coloration of the drainage water or for facilitating release from drying rolls. Starch is often included to improve strength.
Process improvement is particularly desired in retention, drainage and drying, or de-watering, and in the formation, or structure, properties of the final paper sheet. Some of these parameters are in conflict with each other. For instance if the fibers are flocculated effectively into relatively large conventional flocs, this may trap the fiber fines and filler very successfully, so as to give good retention and a porous structure so as to give good drainage. However, the porosity and large floc size may result in rather poor formation, and the large fiber flocs may tend to hold water during later drying stages such that the drying properties are poor. This will require excessive amounts of thermal energy to dry the final sheet. If the fibers are flocculated into smaller and tighter flocs, drainage will be less satisfactory and retention may be less satisfactory, but drying and formation will be improved.
Conventional practice therefore has resulted in the paper maker selecting additives according to the parameters he judges to be the most important. If, for example, increased filler retention is more important to the papermaker than increased production, a polyacrylamide or other very high molecular weight flocculant may be used. If increased production is more important than increased retention then a coagulant, such as aluminum sulphate, may be chosen. Impurities in the stock create additional problems and necessitate the use of particular additives.
It is conventional to include in the stock an inorganic additive and an organic polymeric material, e.g., for improving retention, drainage, drying and/or formation. The prior art adds one to ten percent bentonite and/or one-half to three percent aluminum sulphate to the stock, followed by two-hundredths to two-tenths percent of a cationic polymer, e.g., polyethylene imine, to improve de-watering in the presence of impurities in the stock. Other prior art processes add bentonite to the stock which may be followed by aluminum sulphate or other acidifying substance. Also, attapulgite can be added and alum and/or auxiliary filler retention material can be incorporated. Sometimes a stock containing alum and pigmentary clay is formed and cationic polymer is added.
There can be a significant variation in the type and amount of clays and other materials used in paper. These non-ink components, after ignition of the paper, are commonly referred to as ash content. For example, in some types of newsprint, ash content is less than one percent, and there is no intentional addition of clays to enhance desired properties. In some paper types a small amount of talc may be used in production to help control pitch deposits. Titanium dioxide may be added to improve gloss and color. In better quality newsprint addition of five percent clay and other materials by overall weight is common and in some cases much more.
The market for pigmented coated papers is growing extremely fast, currently about ten to fifteen percent per year, and it may be predicted that even the lower grades such as newsprint will be coated one way or another in the near future.
It will be evident to those skilled in the applications in this area of pigments and fillers that many more industries will have a use for this invention. To name some, the paint, ink, plastics and laminates industries use such pigments and fillers in significant quantities.